The present invention relates to a printer, such as one for an electronic cash register (hereinafter referred to as ECR) and particularly to an improvement in a paper feeding apparatus in a printer enabling selective printing on either an uncut (continuous) sheet or a cut sheet.
Conventionally, ECR printers contain two parallel rolls of uncut sheets with their unwound parts placed over a platen. One of the rolls is for receipt and the other roll is for journal. The two rolls of the uncut sheets are fed by feed rollers, and printing is conducted by a printing head which is mounted on a carriage, so that the tip of the printing head is spaced by a gap from the platen. The carriage is moved in parallel with the axis of the platen so that the printing head scans laterally. The printed part of the uncut sheet for receipt is severed for handling to a customer as a receipt. The printed part of the uncut sheet for journal is wound on a reel as a record or a journal.
An example of a paper feeding mechanism for such an ECR printer is shown in FIG. 13 and FIG. 14. A carriage 1 carries an ink ribbon cassette 2 and a printing head 3 and is guided by both a guide shaft 4 and a guide rail 5 to move in parallel with the axis of a first platen 7 and the axis of a second platen 10. The first and the second platens 7 and 10 are disposed side by side and are capable of rotation independently of each other. An uncut sheet 6 for a receipt is placed over the first platen 7 and is held between the first platen 7 and a pressure roller 7a. A cutter 8 is arranged above the first platen 7 for severing the receipt sheet 6. A journal sheet 9 is held between the second platen 10 and a pressure roller 10a and is guided by a guide bracket 11 and then wound by a take-up reel (not shown) at a rear portion of the printer. A platen gear 12 is fixed to one end of the first platen 7, and is coupled to a stepping motor 16 via an idle gear 14. Similarly, a platen gear 13 is fixed to one end of the second platen 10, and is coupled to a stepping motor 17 via an idle gear 15. To feed either the receipt sheet 6 or the journal sheet 9 the corresponding one of the stepping motors 16 and 17 is actuated. To feed both the receipt sheet 6 and the journal sheet 9 simultaneously, both of the stepping motors 16 and 17 are actuated.
The conventional ECR printers are designed to feed and print cut sheets, and thus cannot feed previously cut sheets, and also is not suitable for printing on a previously cut sheet. One reason for this is that a cut sheet is normally wider than the uncut sheet for receipt or journal, and two platens are placed side by side with a gap therebetween, although such gap may be very small. Moreover, because the two platens must be rotated independently of each other, the structures for supporting them are complicated. Furthermore, the electric power supply must have a larger capacity so that two stepping motors can be energized simultaneously.